Highway radio communications system



Sheet INVENTOR JOHN R McKENNA A'IT RNE'Y Jan. 21, 1969 Filed March 25,1966 HIGHWAY RADIO COMMUNICATIONS SYSTEM Filed March 25, 1966 Sheet 3 of5 INVENTOR JOHN R. McKENNA BY 6 I :7; 5 g

Y A'ITO Jan. 21, 1969 Filed March 25, 1966 J. R. MCKENNA HIGHWAY RADIOCOMMUNICATIONS SYSTEM Sheet 3 JOHN R. McKENNA ATTORNEY United StatesPatent 9 Claims ABSTRACT OF THE DISCLOSURE A highway ratiocommunications system for transmitting a radio signal to vehiclestraveling along a roadway having a radiation antenna means or a pair ofradiating antennas each in the form of a transmission line runningparallel to and on opposite sides of the roadway, and being driven inappropriate phase relation by a radio signal from a common transmitter,with each antenna having a radio signal shield on the side away from thehighway wherein each shield includes an electrically grounded portiondefining a vertical plane extending from at least the plane of theroadway to a predetermined distance above the respective radiatingantenna and acts to attenuate the rearward field of the adjacentrespective radiating antenna as well as the forward field of theradiating antenna on the opposite side of the roadway.

This invention relates to radio communications apparatus and moreparticularly to a highway radio communications system for transmittingradio signals to vehicles traveling along a roadway.

Many systems are known to those skilled in the art for transmittingmessages to vehicles moving along a highway for alerting the driver asto various road con ditions, weather, traffic and the like. Most, if notall, of these systems are adapted to make use of the standard broadcastradio receiver normally carried by the vehicles. Further various typesof transmission apparatus are known for radiating these messages to thevehicles. Some systems employ an embedded transmission line in theroadway which extends along its length. Other systems utilize telephoneand power transmission lines running along the roadway. Still othersystems utilize various other types of antenna means such as simple loopantennas selectively positioned along the highway route.

All of these known systems, however, suffer from an inherent limitationinsofar as actual use is concerned due to the fact that such systemseither transmit too little power or fail to meet the requirementsspelled out in the Rules and Regulations of the Federal CommunicationsCommission (F.C.C.). The Rules and Regulations of the F.C.C., aspresently written, make no provision for a highway radio service.Consequently, this operation must be in accordance with Part of theCommissioners Rules which concerns unlicensed radiation. The regulationsof Part 15 place stringent limitations on the amount of permissibleradiation. The maximum amount of radiated energy is expressed byformulae in which the reference distance is 100 feet. While radiation ispermitted throughout the spectrum, the region of present interest is thestandard broadcast band where the maximum signal strength, at theaforesaid 100 foot distance, is equal to 24,000 (microvolts permeter)/frequency (in kilocycles per second). The permissible level ofradiation in the standard broadcast band varies over approximately a 3to 1 range depending upon the emission frequency. It can be seen thatfor maximum signal strength, the operating frequency should be as low aspossible; however, the present standard broadcast band prohibitsfrequency allocations lower than 535 kilocycles. Assuming Patented Jan.21, 1969 operation around 635 kilocycles, the permissible radiation atone hundred feet away from the radiator is 24,000/635=37.8 microvoltsper meter. This radiation level increases linearly as the distancedecreases, doubling as the spacing is reduced to fifty feet andincreasing ten-fold when the interval is reduced to ten feet.

The sensitivity of the poorest quality auto radio receivers and thenormal varying ambient noise levels along the route determines thelowest values of signal which will provide acceptable listenableservice. It is obviously desirable to provide signal strength in excessof the minimum acceptable level to assure high quality, noisefreereception. To do so will require an unconventional radiation system fora dual lane road bed in which the energy level across each dual lanestrip is maximized while the signal on either side of the right of wayis suitably attenuated.

It is an object of the present invention, therefore, to provide animproved radio communications system for transmitting messages tovehicles moving along a highway.

It is another object of the present invention to provide a high quality,noisefree highway or turnpike communi cations system for vehicles inwhich the transmitted signals are confined to the vicinity of theroadway.

It is yet another object of the present invention to provide arestricted radio transmitting system for communicating to vehiclestraveling along the roadway in a predetermined direction whileattenuating the signal strength to the required level outside of theimmediate vicinity of the roadway.

It is still another object of the present invention to provide a highwayradio communications system which satisfies the requirements of theFederal Communications Commission.

These and further objects of the invention are accomplished by the useof a pair of radiating antennas, each being in the form of atransmission line running parallel to the roadway on opposite sidesthereof, and being driven in appropriate phase relation by a radiosignal from a common transmitter, with each antenna having its ownshield on the side away from the highway wherein each shield acts toattenuate the rearward field of the adjacent radiating antenna as wellas the forward field of the radiating antenna on the opposite side ofthe highway.

Other objects and advantages of the present invention will be morereadily understood when the following detailed description is read inconnection with the accompanying drawings, in which:

FIGURE 1 is a plan view of sections of a pair of oppositely conductingdual lane roadways with a median strip including the embodiment of thesubject invention;

FIGURE 2 is an enlarged front sectional view of one of the dual lanes ofa divided roadway including the subject invention;

FIGURE 3 is an enlarged perspective view of a portion of one of thesingle wire transmission lines and its adjacent associated radiationshield;

FIGURE 4 is an enlarged vertical sectional view of a portion of thesupporting structure upon which each radiating transmission line ismounted;

FIGURE 5 is an enlarged fragmentary side elevational view of anillustrative example of the manner in which the shield wires as shown inFIGURE 3 are attached to the supporting structure;

FIGURE 6 is a perspective view similar to FIGURE 3, but on a reducedscale, showing a modified form of supporting structure for the system ofthe invention;

FIGURE 7 is an enlarged side elevational -view, part ly in section, offragmentary portions of the support of FIGURE 6; and

FIGURE 8 is a cross-sectional view, on a reduced scale, similar toFIGURE 2, showing a modified arrangement of the system of the inventionon a divided roadway.

Referring now to the drawings, FIGURE 1 illustrates the system embodyingthe subject invention. A pair of dual lane roadways 10 and 12 is showncomprising a two direction turnpike such that roadway 10 carries vehicle14 in one direction while the roadway 12 carries the vehicles 15, 16 and17 in the opposite direction. A median strip 26 is adapted to separatethe two roadways. The radio communications system hereinafter disclosedaffords communications to vehicles traveling in a predetermineddirection, that is, one message can be directed to vehicles traveling inone direction on the highway or turnpike while another message can besimultaneously transmitted to vehicles traveling in the oppositedirection. Furthermore, the electromagnetic radiation is substantiallyconfined to the area of the particular roadway to be radiated. It alsoprovides for means whereby a particular message can be transmitted tovehicles along a selected distance such that while a vehicle istraveling along a certain stretch of roadway, one message will becommunicated thereto; however, when passing on to another stretch ofroadway, a second message individual to that section of roadway can betransmitted thereto. It should be understood, however, that when desiredone message can be transmitted to two or more sections ofthe roadway orfor the entire length, depending upon the nature of the message desiredto be transmitted.

In order that different messages can be transmitted to vehicles passingin opposite directions, each roadway 10 and 12 contains its owncommunications system. Each roadway, for example roadway 10, includes atransmitter 22 operating in the broadcast band having an input terminal24, coupled to a two wire transmission line comprising antenna wires 26and 27 running substantially parallel to the dual lane roadway 10 for apredetermined distance Where a second independently operatingtransmitter 22' is located. The transmitters 22 and 22' commonly feedthe antenna wires 26, 27 and 26' and 27, respectively, such that thecurrent in its pair of antenna wires is in appropriate phase relationwith each other, for example, such as substantially out of phase.Terminations, not shown, are coupled to the antenna wires at theirextremities.

It is contemplated that the radiating transmission lines comprising thewires 26 and 27 would run along the roadway 10 for approximately ten totwenty miles or other selected distance. It is desirable for radiatingantennas of such a length that one or more signal amplifiers 28 becoupled to each line intermediate the ends thereof. It is also desirableto include signal amplifiers of the type shown for impedance matchingpurposes where the antenna wires 26 and 27 would have to be fed throughunderground conduits where access roads lead onto the roadway. Inaddition, relatively short breaks in the antenna and shield system, tobe described, are provided at regular intervals along the length of thesystem to enable maintenance equipment such as grass-cutting apparatusto have easy access to both sides of the radiation shields 30 and 32.

A first radiation shield 30 is located behind the roadway 10 and theantenna wire 26 such that it runs parallel thereto and substantiallycoextensive with the antenna wire 26. A second radiation shield 32 islocated behind the other side of the roadway 10 and the radiation wire27 such that it also runs parallel to and coextensive therewith. Thepurpose of the radiation shields 30 and 32 is to attenuate the rearwardfield of the adjacent radiating antenna 26 and 27, respectively, whileat the same time attenuating the forward field of the radiating antennaon the opposite side of the roadway, that is, wires 27 and 26.

The transmitters 22 and 22' are coupled to a source of input signals,not shown, by means of the input terminals 24 and 24, respectively. Theinput signal source may be,

for example, a telephone line containing programmed material in the formof a message to be communicated to a vehicle traveling along theparticular stretch of roadway; however, when desirable, the same inputsignal could be applied to both input terminals 24 and 24'. It should bepointed out that this is stated by way of example only and is not meantto be interpreted in a limiting sense.

The system thus far has been described with respect to a radiocommunications system for the roadway 10. With respect to the roadway 12which carries vehicles in the opposite direction, the apparatus ismerely duplicated with transmitters 22 and 22 coupling signals to theantenna wires 26 and 27 which run adjacent to and parallel to theroadway 12 with the radiation shields 30 and 32 situated behind wires 26and 27 for confining the radiation to the vicinity of the roadway 12while attenuating this signal rearwardly of the antenna wire 26 and wire27. However, it is to be understood that the system can also be used ona two lane undivided roadway.

Referring now to FIGURE 2, there is shown a cross sectional view of atypical 20 foot dual lane roadway in one direction including the twoantenna wires 26 and 27 and a pair of radiation shields utilizedtherewith. Shown in cross-sectional view is a two lane roadway, forexample roadway ltl, having two vehicles 36 and 38 traveling sideby-sidein the same direction along the roadway. The transmitting antenna wires26 and 27 are shown mounted on electrically conductive supportingstructures 40, constructed of metal or the like, comprising the verticalmember 42- and two horizontal members 44 and 46. The antenna wires 26and 27 are attached to but insulated from the horizontal members 44 bymeans of insulating members 48. The antenna-shield configuration islocated on r each side of the roadway 10 such that it is spaced from therespective edges thereof in conformity to terrain and radiationrequirements. Both antenna wires 26 and 27 are located substantially thesame height above the road level as well as back from the respectiveedge of the roadway, preferably an equal distance. For example, if eachlane of the dual lane roadway 10 is ten feet wide, the antenna wires 26and 27 are located approximately ten feet from the respective edge wherethe terrain is relatively flat. However, in certain situations, whereterrain or structures such as bridges, un-derp asses, ovenpasses, andthe like, do not permit relatively wide and fiat shoulders adjacent theroadway the antenna-shield configuration may be placed substantiallycloser to the edge and in a somewhat modified configuration for therelatively short distance required, to satisfy the particular problempresented by roadway construction and route.

The radiation shields 30 and 32 shown in FIGURE 1 each comprise aplurality of wires 30a30g and 32a-32g. The vertical member 42 of thesupport 40, shown in FIGS. 25, is constructed of galvanized pipe orother electrically conductive material, as well as the horizontalmembers 44 and 46, The shield wires 30a-30g and 32a- 32g are adapted toprovide an electrical shield on three sides of the antenna wires 26 and27. The uppermost shield wires 30b and 32b are raised off the ground toaheight preferably of about 10 feet high so that they extend above thetops of the vehicles 36 and 38. The wires 26 and 27 then are mountedapproximately five feet above the surface of the ground. The shieldwires 30a and 32a are offset from the vertical member 42 while theshield wires 30g and 32g are embedded in the ground. The shield wires30b30f run substantially parallel to one another through the verticalmember 42 and define a substantially vertical plane with respect to theground. The same may be said with respect to the shield wires 32b-32f.Ground wires 30a and 301) are substantially parallel to one another anddefine a substantially horizontal plane with respect to the surface ofthe ground. Also shield wire 30a, antenna wire 26 and shield wire 30gdefine a second substantially vertical plane with respect to the earth.Considering the shield wire 32a, the antenna wire 27 and the shield wire32g, they also define a second vertical plane with respect to thevertical plane defined by shield wires 32b-32 Considering now FIGURE 3,there is shown in perspective view one supporting structure 40 for theantenna wire 26 and the shield wires Silo-30b. The vertical member 42which is an electrical conductor is embedded in a concrete base 50 forsupport and is further electrically connected to a grounding rod 52 bymeans of an electrical conductor 54 soldered to the member. Thehorizontal members 44 and 46 are mechanically and electrically coupledthereto such that the member 44 is located midway while member 46 islocated near the upperextremity thereof. The antenna wire 26 is shownmounted to the horizontal member 44 but is insulated therefrom by meansof an insulating member 48 which is preferably a piece of fiberglass rodor the like. The shield wires 30a30f are adapted to pass through themembers 42 and 46 by means of holes drilled therethrough. These wiresare electrically grounded to the members 42 and 46 in a manner to bedescribed in greater detail subsequently.

As has been noted above, the shield wires 30a-30g and 32a32g runsubstantially parallel with each other and parallel to the respectiveantenna wires 26 and 27 and coextensively therewith. In certaininstances, the shield wires 30g and 32g embedded in the earth can beeliminated, such as for example when the antenna-shield configurationpasses over salt water in which case the salt water acts as a shield.

It has been found that a desirable number of shield wires appearing inthe vertical plane above the roadway level as defined by shield wires30b30f and 32b32f should be no less than five for a proper attenuationof the rearward radiation field of the antenna wires 26 and 27 whenoperating in the standard broadcast band but it is to be understood thata greater number of shield wires may be provided. Also, it has beenfound that a desired distance between supporting structures 40 should beroughly eighty feet. With an antenna-shield configuration as shown inFIGURES 2 and 3, the system provides a ratio of the desired signalstrength at the center of the dual lane to undesired signal at adistance of one hundred feet from the closer radiating wire ofapproximately 18:1 which means for 37.8 microvolts per meter undesiredsignal level at one hundred feet a 680 microvolts per meter signalstrength appears at the center of the roadway.

FIGURE 4 discloses in greater detail the mechanical features of thevertical member 42 and the horizontal member 44. The vertical member 42is shown in a sectional view with the horizontal member 44 coupledthereto by means of a threaded coupling into a sleeve 56 which is weldedto the member 42. Reference character 58 indicates a weld. A small hole60 appears in the side of the pipe so that a shield wire, such as 30d or32d, can pass therethrough. The glass fiber rod 48 fits into the member44 and is fastened thereto by means of nut-bolt combination 62. A hole64 appearing near the extremity of the fiberglass rod 48 is adapted topass and support an antenna wire such as antenna wires 26 or 27therethrough.

Referring now to FIGURE 5, there is shown the manner in which the shieldwires 30b-3Gf and 3217-32 are mechanically and electrically coupled tothe vertical supporting structures 40. A shield wire, for example shieldwire 30b, is continuous and passes through the vertical member 42 bymeans of the holes 60. A tension relieving wire 66 is wrapped tightlyabout the shield wire 30b immediately adjacent the holes 60 and a solderconnection 68 is made at each wrap to the member 42 which, as has beensaid before, is preferably composed of galvanized pipe. A third solderconnection 69 is made between the tension relieving wire 66 and themember 42 intermediate the solder joints 68.

\Vhat has been shown and described therefore is a turnpike radiocommunications system for vehicles traveling in a predetermineddirection along a turnpike. The system comprises in combination witheach roadway one or more transmitters commonly coupled to a two wireantenna system with one wire each running on opposite sides of theroadway for a predetermined distance. Secondly, and most importantly,each line of said transmission line comprises a radiating antenna wirerunning substantially parallel to and adjacent the roadway with eachantenna line being substantially shielded on three sides by a pluralityof shield wires running substantially parallel to and coextensive withthe transmission line. Both transmission lines are commonly driven bythe transmitter such that the signals traveling on the transmissionlines are in ap-.

propriate phase relation, the resulting effect being that the radiationshields attenuate both the rearward field of the adjacent radiatingantenna as well as the forward field of the radiating antenna on theopposite side of the roadway.

This invention has been shown and described in connection with the mostfavorable terrain adjacent the edge of the roadway. However, ininstances such as in built-up highways, where a roadway shoulder is onlya few feet wide, not sufiicient for a vehicle to pull ofi the roadway,with the terrain then falling off on a steep decline, the verticalmembers 42 of the supports 40 would be substantially longer since theywould be anchored in the ground a substantial distance below the levelof the roadway and would still extend the same distance above theroadway surface as shown. In such an instance, additional shield wirescomparable to wires 30a30g and 32a-32g would be connected on thesupports to form a radiation shield adjacent the roadway extending thevertical dimension of the supports. This means the supports would alsoprovide shield wires at levels below the level of the highway, that isbetween the highway level and the plane at which the support contactsthe ground. The supports would still provide, for example, at least fiveshield wires above the roadway level.

Other variations in the supporting struture, not shown, may becomenecessary to form a continuous radiation shield adjacent the roadway inother peculiar terrain, bridges, etc., situations, but the concept ofthe invention remains the same in all instances.

A modified form of support 40 constructed of electrical insulationmaterial, such as fiber glass, is shown in FIGURES 6-8, with FIGURE 8also disclosing a modified support 70 for use in the center strip ormedian of a divided highway where the median is not wide enough toaccommodate a pair of radiation shields as shown in FIGURE 1. Thesupporting structure 40 is similar to the supporting structure 40 andthe members connected thereto, as previously described, and similarcomponents are designated by corresponding primed numerals in thedrawings. In this form of the invention, vertical member 42' isconstructed of insulation material, such as plastic or fiber glasstubing, and is appropriately apertured to receive horizontal rod members44 and 46' therethrough which are secured thereto by appropriate means,such as epoxy resin, as indicated at 71. Rod members 44' and 46' arealso constructed of electrical insulation material, such as fiber glass,and are apertured adjacent the ends to pass and support antenna wires26" or 27", and shield wire 30a or 32a, respectively. In like manner,vertical member 42 is provided with a plurality of apertures along itslength through which shield wires 30b- 30f or 32b'32f pass. The wires30a-30f or 32a'-32f', forming the radiation shield, are electricallygrounded by means of an electrical conductor 54' electrically connectedto grounding rod 52 and each of the shield wires at 72, by soldering,clip connectors, or the like. Where necessary, conductor 54 may besecured in position by means of tape 73, or other suitable means. Thetop of vertical member 42' is provided with a cap 74 connected theretoby suitable means, such as epoxy, to close the end of the tube.

Where circumstances permit, as where the median of a divided highway isrelatively small as previously indicated, a single supporting structure70 may be used for supporting a pair of antenna wires 27" and a pair ofupper shield wires 32a as indicated in FIGURE 8. In this arrangement thevertically arranged shield wires 32b'32f serve as the vertical shieldwires for the communication systems, of both roadways 10 and 12, butelectrically the system remains the same as when a pair of completeradiation shields are provided in the media. The upper and lowerhorizontal rods are the same as rods 46' and 44 but extend substantiallythe same distance from opposite sides of the vertical member 42 andrespectively support shield wires 32a and antenna wires 27" at each endthereof. The wires are connected into the system as before, except inthis instance a pair of shield wires 32a and shield wires 32b'32f areconnected to ground by a conductor 54' at each of the support members.

While there has been shown and described what is at present consideredto be preferred embodiments of the subject invention, modificationsthereto will readily occur to those skilled in the art. It is notdesired therefore that the invention be limited to the specificarrangements shown and described but it is to be understood that allequivalents, alterations and modifications within the spirit and scopeof the present invention are herein meant to be included.

I claim as my invention:

1. A highway radio communications system for transmitting a radio signalto one or more vehicles traveling along a roadway comprising incombination: a radio communications transmitter having an input signalcoupled thereto from a signal source; radiation antenna means, coupledto said radio communications transmitter for radiating a radio signal tosaid vehicles, and extending a predetermined distance along said roadwayand being located substantially parallel to and adjacent thereof; and apair of radio signal shield means, one on each side of and substantiallyparallel with said roadway, substantially coextensive and parallel withsaid radiation antenna means; said radiation antenna means located'between at least one side of said roadway and one of said radio signalshield means; and each radio signal shield means including anelectrically grounded portion extending vertically from at least theplane of said roadway to a predetermined distance above said radiationantenna means for attenuating said radio signal to a predetermined levelin directions laterally away from said roadway thereby confining saidradio signal to the immediate vicinity of said roadway.

2. A radio communications system as defined in claim 1, wherein saidradiation antenna means comprises at least a one wire transmission linelocated a predetermined height above the surface of the roadway.

3. A radio communications system as defined in claim 1, wherein saidradiation antenna means comprises two radiating antenna wirescoextensive with each other, commonly fed from said radio communicationstransmitter so to carry substantially out of phase signal currents anddisposed relative to said roadway such that one wire is situated on eachside thereof between the roadway and the radio signal shield means.

4. A radio communications system as defined in claim 1, wherein saidradiation antenna means comprises a two wire transmission linecoextensive with each other, commonly fed from said transmitter andbeing disposed relative to said roadway such that one wire is located oneach side thereof; and additionally including radio signal amplifiermeans selectively coupled to each line of said two wire transmissionline intermediate the ends thereof for boosting the signal strength ofsaid radio signal to a predetermined level.

5. A radio communications system as defined in claim 1, wherein saidpair of radio signal shield means each comprises: a plurality ofsupporting structures having grounding means; a plurality ofhorizontally extending shield wires substantially parallely disposed anddefining a substantially vertical plane extending from at least theplane of said roadway to a predetermined distance above said radiationantenna means and being supported and connected at selected horizontalintervals to one of said plurality of supporting structures andgrounding means; and at least one shield wire mounted on and connectedto said one supporting structure and positioned away from said pluralityof shield wires toward said roadway such that it is substantiallycoplanar with one shield wire of said plurality of shield wires.

6. A radio communications system as defined in claim 1, wherein saidpair of radio signal shield means each comprises: a plurality ofsupporting structures; a plurality of substantially horizontallyextending shield wires defining a substantially vertical plane extendingfrom at least the plane of said roadway to a predetermined distanceabove said radiation antenna means and being supported at selectedhorizontal distance intervals along said roadway by one of saidplurality of supporting structures; at least one shield wire mounted onsaid one supporting structure and positioned away in offset relationshipfrom said plurality of shield wires toward said roadway such that it issubstantially horizontally coplanar with one shield wire of saidplurality of shield wires; and means for electrically grounding all ofsaid shield wires.

'7. A radio communications system as defined in claim 1, wherein saidpair of radio signal shield means each comprises a plurality of shieldwires mounted on an electrically grounded support, said plurality ofshield wires being disposed substantially parallel to the surface of theearth and defining a first substantially vertical plane extending fromat least the plane of the roadway to a predetermined distance above saidradiation antenna means, means for grounding said plurality of shieldwires to said grounded support; said radiation antenna means located apredetermined distance above the surface of the earth; at least oneadditional shield wire mounted on said grounded support and being offsettoward said roadway from said plurality of shield wires and positionedabove said antenna means a predetermined distance such that it defines asubstantially horizontal plane with one of said plurality of shieldwires and a second substantially vertical plane with said antenna means;and still at least another shield wire embedded in the earth apredetermined distance below the ground and intermediate the said firstvertical plane and said roadway.

8. A system as defined by claim 1, wherein said pair of radio signalshield means each comprises a plurality of shield wires strungsubstantially horizontally between supports having grounding meanslocated at selected distance intervals along said roadway, saidplurality of shield wires defining a substantially vertical planeextending from at least the surface of the earth to a predetermineddistance above said radiation antenna means, means for grounding saidplurality of shield wires to said grounding means, at least one othershield wire strung between said supports and adapted to be ofisettherefrom toward said roadway such that one of said plurality of shieldwires and said other shield wire defines a substantially horizontalplane above said antenna means with respect to the surface of theroadway, said other shield wire defining yet another substantiallyvertical plane with respect to the surface of the roadway with saidantenna means; and yet another shield wire embedded beneath the surfaceof the earth running substantially parallel with said other shield wireand said antenna means and lying substantially in said yet anothervertical plane as defined by said yet another shield wire and saidantenna means.

9. A radio communications system as defined by claim 1, wherein saidantenna means comprises a two wire transmission line, forming tworadiating wire antennas running on opposite sides of said roadway,commonly driven from said signal source, supports having grounding meanspositioned at predetermined distances along each side of said roadway,each wire antenna mounted on and insulated from said sup orts on therespective side of said roadway, and wherein said pair of radio signalshield means each comprises a plurality of shield wires mounted on saidsupports and electrically connected to said grounding means and defininga substantially vertical plane extending from at least the plane of theroadway to a predetermined distance above the respective wire antennaand positioned behind a respective wire antenna in relation to saidroadway; at least another shield wire mounted on said supports andelectrically connected to said groundmg means, but ofiset threfrom suchthat it lies in another vertical plane as defined by it and saidrespective wire antenna; and still another shield wire embedded in theearth running parallel and coextensive with said wire antenna and lyingin said another vertical plane, whereby all of said shield wires providea radio signal shield on three sides of each of said radiating wireantennas.

References Cited UNITED STATES PATENTS 1,985,241 12/1934 Daya 34384l X2,980,793 4/1961 Daniel 325129 3,105,119 9/1963 Cary et al 32526 ROBERTL. GRIFFIN, Primary Examiner.

BENEDICT V. SAFOUREK, Assistant Examiner.

U.S. c1. X.R.

